Electrical musical instrument keying system



Miilch 25, 1969 R. B. scHREcoNGosT 3,435,123

l ELECTRICAL MUSICAL INSTRUMENT KEYING SYSTEM .filed may 24, 1965 sheetof 2 March 25, 1969 R. B. scHREcoNGos-r 3,435,123

ELECTRICAL MUSICAL INSTRUMENT KEYING SYSTEM Filed May 24, 1965 sheet 2of 2 VOL T465' N `20V 20H5 /ams 'sa'.

50,445 -r/ME fppeox//wz rs) United States Patent O U.S. Cl. 84-1.26 6Claims ABSTRACT F THE DISCLOSURE An electrical musical instrument keyingsystem which provides double diode keyers for each signal source to bekeyed. All keyers are normally held off by a common bias voltage whichis variable, and are turned on individually by a keyed counter voltagewhich overcomes the bias voltage for the particular keyer. RC timingcircuits are used to control decay subsequent to disconnection of thekeying voltage source. Decay rate is variable depending upon theselected level of the common bias voltage. Variations in the basicsystem include provision of a dual slope decay envelope by the additionof a resistor and Vdiode connection in the RC timing circuit and theprovision of two types of percussion by the incorporation of RC anddiode connections in the keying circuits.

This invention relates generally to electrical musical instruments suchas electric organs and similar toneproducing devices, and is moreparticularly related to apparatus for controlling the decay rates ofmusical tones produced by such instruments. The invention is concernedmore specifically with controlling the operation of keying circuitsemployed in electric organs or other key-actuated electrical musicalinstruments whereby the rate of change in amplitude of tone signals maybe controlled so that the sounds produced by such signals may be made todecay from their maximum strength at predetermined rates within thecontrol of the player. By means of the invention, therefore, a varietyof pleasing and interesting tonal elfects may be produced affecting themood of the music being played and subject to selection by the player.

Although electric organs have previously been made wherein the rate ofdecay of the notes played was subject to a certain amount of control bythe player, so far as I am aware such devices have been limited for themost part to systems requiring a large number of expensive electricalcomponents and complex switches, and thus were not economically suitablefor many commercial uses.

It is therefore a broad object of this invention to provide simple andinexpensive apparatus for use with electrical tone-producing instrumentswhich permits control by the player over the rate of decay of notesplayed by the instrument.

It is a further object of the invention to provide apparatus of the type-mentioned in the foregoing object which is capable of selectivelyproviding long and medium sustain and substantially instantaneous stopplaying by adjusting one voltage in a system of many keyers used in theinstrument.

A further object of the invention is to provide means for controllingthe potential at a terminal in a keyer used in an electrical organsystem wherein the keyer is connected between a tone signal source andthe organ output system, and wherein the keyer is capable of changingthe amplitude characteristics of the signal supplied to the outputsystem depending on the potential applied to such terminal in the keyer.

Other objects, advantages, and features of this invention will beapparent from or pointed out in the following specification consideredin connection with the accompanying drawings showing a preferredembodiment of the invention. In the drawings, wherein like numeralsrefer to the same or similar parts in the several figures:

FIG. 1 is a diagrammatic representation of a keying system of akeyer-operated electrical musical instrument, including a preferred formof keyer and showing preferred means in accordance with the presentinvention for controlling the rate of decay of electrical signalstransmitted by the keyer to its output conductor;

FIG. 2 is a more general diagrammatic represenation of a keying systemof an electrical musical instrument illustrating the use of amultiplicity of keyers of the type shown in FIG. 1 and the manner inwhich the decay rates of electrical signals transmitted by suchindependent keyers are controlled as a group by a single control meansin accordance with the present invention;

FIGS. 3, 4, and 5 are diagrams illustrating the rate of change in thedecay characteristics of electrical tone signals supplied by a keyer ofthe type shown in FIG. 1 to its output conductor, under several modes ofoperation.

FIG. 6 is a diagram of a network adapted to be substituted for acomponent of the system shown in FIG. 1, for improving the performance0f the system;

FIG. 7 is a diagram comparing the decay characteristics illustrated inFIG. 5 with the `decay characteristics of electrical tone signalssupplied to the Output system fby a keyer modified by inclusion of thenetwork of FIG. 6, under two modes of operation;

FIGS. 8 and 9 are diagrams showing networks which may be substituted fora component of the system shown in FIG. 1, for providing different modesof operation of the system.

Referring now particularly to FIG. l, the invention is therediagrammatically illustrated as incorporated in the circuit of anelectric organ of the type in common use wherein an individual tonesignal source is provided for each of the audio-frequency signalscorresponding to the notes within the range of the instrument. Such tonesignal sources may be of any suitable type, such as electronicoscillators, with or without associated frequency dividers, forinstance. In the embodiment shown in the drawing it will be considered,in the interest of being specic, that the invention is applied to asingle manual keyboard having electronic generators as the source of theaudiofrequency signals. It will, of course, be understood that theinvention is applicable to more than one organ keyboard, including, ifdesired, a pedal keyboard.

In FIG. 1 there is shown a tone signal source 10, such as an electronicoscillator, coupled through a lead 12 to a keyer shown enclosed in a boxand indicated generally at 14. The keyer 14 includes a high impedanceelement or resistor R16 in series with a 'resistor R18 of lowerresistance, the common connection 20 of these resistors being connectedby a lead 22 to one side of a diode 24. The remote end of the resistorR16 is connected to the lead 12, and the remote end of the resistor R18is connected by a lead 26 to a common lead 28 connected to a source oflow, preferably negative, potential, for example 0.15 volt. In serieswith the diode 24 is a second diode 30, the other side of which in turnis connected through an output conductor 32, containing a resistor R34,to a common lead 36 to the output system of the instrument, the lead 36being grounded through an impedance element such as a resistor R37. Theoutput system of the instrument is not shown since it does notconstitute part of the present invention, but it may be of conventionaldesign including electroacoustical translating means for translatinginto sound the signals supplied to the lead 36.

Also connected to the common lead 36 are a plurality of other resistors,such as R34', R34", and R34 corresponding respectively to the resistorR34 and illustrative of such resistors in all of the other keyers in theorgan system. The diodes 24 and 30 are disposed back-to-'back and areoriented in the circuit to pass direct current outwardly from a commonterminal 38 between them, and each diode becomes conductive to analternating current signal when the potential on the terminal 38 exceedsthe extinction potential of the diode. The diodes 24 and 30 thusconstitute a variable impedance signal transmission device which isnormally non-conductive, but which becomes conductive when the potentialat the terminal 38 exceeds the extinction potential of the diodes.Accordingly, the amplitude characteristics of the tone signaltransmitted through the diodes to the instrument output system aredependent upon the potential applied to the terminal 38. In theembodiment being described, the diodes 24 and 30 have equal extinctionpotentials of 0.6 volt. Diodes suitable for this purpose are the typicalsilicon junction diodes of commerce.

The terminal 38 is connected through a resistor R40 of high resistanceand a resistor R42 of low resistance, in series, and through a lead 44to a switch 46 by which the keyer may be connected to a common lead 48connected to a source of positive potential; for example, -I-3 volts.The switch,y 46 is adapted to be operated by a playing key (not shown)of the organ in well known manner; that is, the pressing or actuating ofthe associated playing key closes the switch 46, whereby the potentialat the termin-a1 38 is raised above the extinction potential of thediodes 24 and 30, rendering them conductive, and thus conditioning thekeyer to transmit to the organ output system a signal corresponding tothat provided by the signal source 10. Conversely, releasing suchplaying key opens the switch 46, causing the potential at the terminal38 to drop below the extinction potential of the diodes, rendering themnon-conductive, whereby passage of such signal to the organ outputsystem is discontinued, as will be more fully described hereinafter.

The junction or common connection 50 to resistors R40 and R42 isconnected through a capacitor C52 to a source of bias potential belowthe extinction potential of the diodes 24 and 30, such as ground. Thejunction 50 is also connected through a resistor R54 of high resistanceand a lead 56 to a common lead 58 connected to the blade 60 of a stepswitch 62 having a plurality of terminals, here shown as three, i.e.,terminals 64, 66, and 68, connected respectively to sources of differentpotential each of which potentials is lower than the aforementionedextinction potential, but none of which is higher than that of the saidbias potential sour-ce connected to the capacitor C52. The sources ofpotential connected to the said terminals 64, 66, and 68, may be, forexample, -20 volts, -3 volts, and ground potential. Also connected tothe common lead 58 are a plurality of other resistors, such as R54',R54, and R54'", corresponding respectively to the resistor R54 andillustrative of such resistors in all of the other keyers in the organsystem.

Referring to FIG. 2, there is illustrated diagrammatically an organkeying system employing a plurality of keyers identical to thosepreviously described and shown in FIG. 1, FIG. 2 also showing the mannerin which the keyers are incorporated in the main organ circuit. In FIG.2 the reference numerals for the various parts are the same as thoseused for similar parts in FIGA, with differentiating suiixes a, b, and nto denote groups of assocaited parts, to facilitate the description.

The outputs of the audio-frequency signal generators a, 10b, and 10n arecoupled respectively through their associated leads 12a, 12b, and 12n tokeyers 14a, 14b, and 14n identical to the keyer 14 previouslydescri-bed. Although only three keyers are shown for purposes ofillustration in FIG. 2, it is to be understood that the number of suchkeyers used in the organ system depends upon the number of playing keysin the instrument which have the invention applied thereto.

The keyers 14a to 14n are also connected respectively through theirassociated leads 26a to 26n to the common .15 v. lead 28, through theirassociated leads 44a to 44n to the playing key switches 46a to 46n, andthrough their associated leads 56a to 56n to the common control lead 58.The keyers 14a to 14n are likewise connected through their respectiveassociated output conductors 32a to 32a to the common lead 36 connectedto the instrument output system.

In an organ system in which the amplitude of the signals supplied to thekeyers is about 1.5 volts and the potentials supplied to the lines `28,48, and 58 are =as indicated above, I have found that good results areobtained when the components of the keyers have the following values,wherein the resistances of the resistors are in ohms (K representing1000):

Component: Value R16 47K R18 4700 R34, R34', R34 2200 R37 1000 R40 33KR42 100 RS4, R54', R54", R54 100K C52 microfarads 20 Operation of thepresent apparatus will now be described With particular reference toFIG. 1, in which description it will be assumed that the values of thevarious components and the potentials supplied to the lines 28, 48, and58 are as described above. When the electric organ is turned on, thetone signal sources supply their respective tone signals at constantamplitude to their associated keyers, and therefore the signal suppliedby the source 10 is impressed on the lead 22 of the keyer 14. Assumingthe amplitude of the signal supplied to the input lead 12 to the keyerto be about 1.5 volts as mentioned above, the signal potential on thelead 22 will be about millivolts, peak to peak.

Assuming further that the switch arm 60 is in contact with the terminal68 to ground, if the player now actuates the playing key associated withswitch 46, thereby closing said switch, a potential of about '0.7 to 0.8volt is impressed on the terminal 38 from the line 48, capacitor C52becoming charged at the same time. Since the potential at the terminal38 thus exceeds the 0.6 Volt extinction potential of the diodes 24 and30, the diodes become conductive, and the tone signal passes through thediodes to the output conductor 32, and thence to the output system ofthe instrument. Transmission of such signal to the output system of theinstrument continues at a constant amplitude as long as the switch 46 isclosed, i.e., as long as the associated playing key isl pressed.Releasing the playing key causes the switch 46 to open, whereupon thecapacitor C52 discharges principally through the resistor R54, somedischarge also taking place through R34, R37 and R18. The signalcontinues to pass through the diodes 24 and 30 to the output system on adeclining basis until the potential at terminal 38 drops to theextinction potential of the diodes, at which time the diodes becomenonconductive and transmission of the signal to the output systemceases. The amplitude of such output signal is therefore progressivelyreduced, and the sound produced therefrom by the output systemcorrespondingly decays as the capacitor C52 discharges. Because of thenegative bias imposed on the lead 22 by its connection through lead 26to the line 28, diode 24 becomes conductive slightly before diode 30when switch 46 is closed, and extinguishes slightly after diode 30 whencapacitor C52 discharges after switch 46 is opened, this mode ofoperation providing a better decay envelope of the signal passing to theoutput conductor 32 than would be obtained if the diodes 24 and 30simultaneously became conductive and then simultaneously extinguished.With the common lead 58 connected to the ground terminal 68 of the stepswitch 62, the decay from maximum voltage to the extinction potential ofthe diode 30 takes about three seconds. This is illustrated in FIG. 3,which shows the relation of voltage at the capacitor C52 to time,following opening of the switch 46, the potential at the capacitordecaying exponentially and rather gradually from the maximum of aboutthree volts to ground potential.

If, in operation of the keying system, the arm 60 of the switch 62engages terminal 66 (-3 volts potential), the decay rate is considerablyfaster than that just described, the decay from maximum potential to theextinction potential of the diode 30 here taking about one second. Thisis illustrated in FIG. 4. FIG. 5 illustrates the much faster decay rateobtained when the arm 60 is engaged with the terminal 64 (-.20 voltspotential) of the step switch, the decay period in this instance beingabout 100 milliseconds. The moment at which transmission of the signalsto the output system ceases is the point shown in FIGS. 3, 4, and 5 atwhich the curve crosses the horizontal line representing the 0.6 voltextinction potential of the diode 30.

If a more rapid decay rate is desired, but it is desired not to exceed-20 v. as a connection for the lead 56, on the ground that this mightproduce an excessive reversing voltage through the switch 62 during theperiodic increase and reduction in potential at the terminal 38, thiscan be accomplished by applying a lower voltage, eg., +1.5 v. instead of+3 v., to the bus 48. This of course reduces the initial signal voltageat the output conductor 32, requiring the output signal to be ampliiiedto a greater degree than is necessary when the bus 48 carries 3 volts.Such additional amplification is of course easily accomplished by meanswell known in the art.

An improved decay envelope shape over that achieved through the use ofthe simple resistor RS4 in the lead 56 may be obtained by substituting adiode-resistor network therefor, one form of which is shown in FIG. 6.Referring to FIG. 6, it will be seen that the network comprises aresistor R70 connected at one end to the junction 50 and at the otherend to the common lead 58. Bypassing the resistor R70 is a secondresistor R72 connected in series with a silicon diode 74 oriented to beconductive when the potential is higher at the junction 50. When thisnetwork replaces resistor R54 having a resistance of 100K, the resistorsR70 and R72 preferably have resistances of 220K and 100K, respectively.

Reference is now made to FIG. 7 which graphically depicts the rate ofpotential drop at the junction 38, and the decay characteristics of thetone signals passing through diode 30 to the output conductor undervarious conditions during discharge of the capacitor C52. As in FIGS. 3to 5, the moment when transmission of the respective signals to theoutput system ceases is shown in FIG. 7 by the intersections of thecurves with the horizontal line representing the 0.6 volt extinctionpotential of the diode 30. In FIG. 7 all of the curves represent theabove-mentioned rate of potential drop and the signal decaycharacteristics produced by having the mode switch blade 60 in contactwith terminal 64 connected to the -20 v. potential source. Curve xrepresents the decay characteristics observed when the energizingvoltage from the bus l48 is +3 volts and the simple resistor R54 ispresent in the lead 56 for discharging the capacitor C52, and shows thatthe potential on the terminal 38 decays to the extinction potential ofdiode 30 (0.6 volt) in about 100 milliseconds. Curve y depicts the decaycharacteristics of the signal under conditions similar to those forcurve x, except that the resistor R54 has been replaced by theresistor-diode network of FIG. 6, and shows that the potential onterminal 38 decays to the extinction potential of diodes 24-30 in about5,0 milliseconds, most of this decay occurring rather quickly. Curve zdepicts the decay characteristics of the signal under conditions similarto those for curve y, except that the energizing voltage supplied by bus48 is +1.5 volts and shows that the potential on terminal 38 decaysquickly to the extinction potential of diodes 24-30 in about 20milliseconds. The decay envelope of the signal improves, it is believed,resulting in a more pleasing musical effect, as the curves drop morevertically initially.

The improved effects obtained by using the resistordiode network of FIG.`6, as just described, may also be obtained by using a non-linearresistor, such as a silicon carbide resistor in place of resistor R54.

In the foregoing description, the invention has been described as usedin conjunction with keying providing sustained playing of a note as longas a key-operated switch is closed. It will of course be understood thatthe invention is also applicable to keying systems providing other modesof operation, such as percussion, or percussion-sustain systems.Modications of the keyer of FIG. l, adapting the keyer for suchpercussion and percussionsustain operation, are shown respectively inFIGS. 8 and 9 and are representative of other forms of keyers with whichthe present invention may be used.

In FIG. 8 the terminal 38 between diodes 24 and 30 is connected throughthe resistor R40 to the junction 50 which is connected through theresistor R54 to the mode switch `62, as described above. In theembodiment here described, however, the junction 50 is connected toground through a capacitor C76, and is also connected through a resistor'R78 to a common connection to a capacitor C80 and one side of a diode82, the other side of the latter being connected to ground. The diode isoriented to be conductive when the common point between C and R78 issufficiently below ground. The capacitor C80 is connected through aresistor R84 to a 3 volt D.C. terminal of the power supply, and thecommon connection to capacitor C80 and resistor R84 is connected througha keyoperated switch 86 to ground. The other components of the keyer,and its connections to the signal source, the output system, the modeswitch 62 and the common lead 28, are all the same as in FIG. lpreviously described. Suitable values for the added components of theembodiment of FIG. 8 are: 1000 ohms for the resistors R78 and R84, .47microfarad for capacitor C76, and 20 microfarads for the capacitor C80.

In operation ofthe embodiment of FIG. 8, upon closing the switch 86 bypressing the playing key associated therewith, the capacitors C76 andC80 become positively charged, and the potential at the terminal 38 israised above the +0.\6 volt extinction potential of the diodes 24 and30, whereupon the signal supplied by the signal source 10 passes throughthe diodes 24 and 30 to the output system of the instrument. Thecapacitors C76 and C80, which have divided the initial charge on C80,immediately begin to discharge, lowering the potential of the terminal38, and the transmission of the signal to the output system stops whenthe potential at terminal 38 drops to the extinction potential of thediode 30, as described above. Note that this effect is due to theinitial charge on C80 which is divided with C76. If the key is held longenough, the decay cycle is automatically completed. If the key isreleased before completion of the decay cycle, the note is extinguishedby reestablishment of the -3 v. connection to the capacitor C80.

FIG. 9 is substantially the same as FIG. 8, except that in the formerthe junction 50 is grounded through a capacitor C88 and a diode 90 isdisposed between the resistor R78 and the common connection to thecapacitor C80 and the diode 82. Diode 90 is oriented to pass currenttoward the junction 50. A suitable value for the capacitor C88 is 20microfarads, and the other capacitors and resistors in FIG. 9 have thevalues given above. Operation of the modification of FIG. 9 is similarto that of the modification of FIG. 8, except that if the key contact 86is opened before completion of the potential rundown at the junction 38,capacitor C88 continues to be eiiective, even though capacitor C80 isdischarged. The note is not immediately extinguished, therefore, as inFIG. 8, but trails off at a more rapid rate than prior to key release.

In all of the embodiments of FIGS. 1, l8, and 9, it is seen that decayof the signal commences upon the cessation of conduction of chargingcurrent to the capacitor or capacitors in the respective keyers. In FIG.l such cessation of charging current is brought about by release of theplaying key, which causes switch 46 to open, whereas in FIGS. 8 and 9the cessation of charging current occurs immediately after thekey-operated switch -86 is closed.

Operation of the general keying system used in playing notes of allfrequencies vvithin the range of the instrument will be apparent fromFIG. 2. Since the keyers 14a to 14n have parallel connections to theleads 28, 36, and 8, and (through switches 46a to `4611) to the lead 48,any number of notes may be played simultaneously by actuating orpressing the playing keys corresponding thereto, which in turn willclose respective associated ones of switches y46a to 46u, and each notewill decay at the rate established by the position (selected by theplayer) of the arm 60 of the step switch 62 when the playing keyassociated with such note is released (FIG. l), or played (FIG. `8), orplayed and released (FIG. 9), in the manner described above. Thus, thepresent invention provides simple apparatus whereby the player canselect any one of a plurality of decay rates for signals supplied to theoutput system by all the keyers in the musical instrument simply bymanipulating a single switching member, this control feature being oneof the important advantages of the invention.

A further advantage of my invention is that it permits the use ofoperating voltages (i.e., the voltages impressed on the terminal 38)which are high relative to the voltage of the tone signal input at thediode 24, 'whereby distortion of the wave form of the signal during thedecay interval may be maintained below the limit of perceptibility tothe ear.

While I have shown and described a particular embodiment of myinvention, it will be apparent to those skilled in the art that numerous-modications and variations may be made in the form rand constructionthereof, without departing from the spirit and scope of the invention.For example, it will be understood that the extinction potentials of thediodes need not be as given, and that they may be higher or lower thanthe above mentioned value of 0.6 volt, and may even have negativevalues. Likewise, the values of the various components of the keyers,and values and signs of the potentials supplied to the lines 28, '48,and S8, are not critical and may be varied, if desired. Such values areall a matter of choice, and one skilled in the `art will readilyunderstand how variations therein will aiiect the operatingcharacteristics of the keying system. It will also be apparent that theinvention is not limited to use with the specific keyer describedherein, but may be used with other kinds of keyers, such as transistorkeyers, tube keyers or keyers containing other solid state devices, inwhich transmission of a signal through the keyer is dependent on thepotential at a given point or terminal therein. I therefore desire, bythe following claims,

to include within the scope of my invention all such modiiied forms ofthe apparatus disclosed herein by which substantially the results of theinvention may be obtained by substantially the same or equivalent means.

I claim:

1. A keying system for an electrical musical instrument having aplurality of tone signal sources covering a musical range of severaloctaves, a common output system, and a plurality of keyers individuallyconnecting the sources to the output system, said keyers individuallycornprising a pair of diodes in series connected between each source andthe output system, said diodes being oriented to pass direct currentoutwardly from a terminal between them, a plurality of DC bias sourcesall below the extinction potential of said diodes, a bias lead common toall of said keyers, switch means for connecting any selected one of saidbias potential sources to said common bias lead to fix the extinctionbias thereon, a timing capacitor for each of said keyers connected tosaid bias lead, each of the capacitor bias connections including animpedance element, za source of keying voltage above the extinctionpotential of said diodes, an actuating circuit including a playing `keyoperated switch and an impedance element connected for applying thekeying voltage to said timing capacitor by way of the last saidimpedance element in opposition to the selected bias voltage on saidcapacitor when said playing key switch is operated, a circuit connectingthe terminal between said diodes to said timing capacitor, the last saidcircuit including an impedance element, :and the value of the capacitorbias impedance element being high as compared with the value of thekeying voltage impedance element.

2. The keying system as called for in claim 1 in 'which all of theimpedance elements are resistors.

3. The keying system Ias called for in claim 1 in which the capacitorbias impedance element is a resistor in parallel with a series connectedresistor and diode.

4. The keying system as called for in claim 1 in which the :keyingvoltage source is a capacitor, means for charging said capacitor andmeans including said playin-g key switch providing a connection fortransferring a portion of the change on the last said capacitor to saidtiming capacitor when said playing key switch is operated.

5. The keying system as called for in claim 4 in which the connectionfor transferring charge from the voltage source capacitor to the timingcapacitor includes means for preventing transfer of charge in thereverse direction.

6. The Ikeying system as called for in claim 5 in which the means forpreventing reverse transfer of charge is a diode.

References Cited UNITED STATES PATENTS 3,196,201 7/1965 McDonald 84-1.263,333,042 7/1967 Brombaugh SLi- 1.26

ARTHUR GAUSS, Primary Examiner.

vROBERT H. PLOTKIN, Assistant Examiner.

U.S. C1. X.R. 84-1.l3

